Traditional long range artillery munitions have been a mainstay of warfare over the centuries. Much effort has been spent attempting to improve upon the accuracy of the projectiles. With the development of semiconductors and the integrated circuits, it has become possible to install embedded controllers to measure in-flight dynamics and to correct for inaccuracies and disturbances as integral components of the artillery rounds.
In terms of accuracy, the dispersion pattern of impact locations increases with the increasing range of projectiles. Factors that contribute to the increased dispersion are winds aloft (meteorological data), propellant temperature variations, and marginal errors in gun elevations. The final dispersion pattern is an elongated ellipse with the major axis in the direction of flight.
Winds aloft present one form of disturbance in that crosswinds can send a projectile left or right relative to the intended target, and head and tail winds can propel the projectile too far or too short of the intended target.
Recently, different propellants have been used, some combust more quickly and propel the projectiles out of the cannon at higher velocities than others. As a result, resources have been dedicated to characterize the different production lots of propellants, as they leave the factory. Ambient temperature also affects the propellant in a gun in that a hot propellant typically produces increased muzzle velocities, while a cold propellant produces lower muzzle velocities.
In addition to external dynamics, there are issues that affect the performance of the electronics installed within the projectiles. For inertial sensors, the severe gun-launch environment often produces permanent bias shifts in the measured acceleration of the projectiles. Additionally, the high spin rate of the stabilized projectiles may also affect the readings on a sensor, by adding spurious centrifugal forces to the sensor that are not, in reality, affecting the projectile.
One method to improve the accuracy of the projectile is to install GPS receivers that input an accurate estimate of the physical location of the projectile into the controller. Additionally, the data from the GPS receivers can be coupled with advanced inertial suites capable of being calibrated and continuously updated throughout the flight of the projectile, to improve performance. U.S. Pat. Nos. 7,500,636 and 7,834,300 are examples of the increasing complexity of integrated systems to guide a ballistic munition.
Separately, the additional confounding of data by the spin-stabilization is to add canards to the fuze, as well as high cost bearings. This combination allows the electronics stored in the fuze to be “de-spun” and acts independently of the spinning of the round.
Previous fuze efforts attempted to correct for the range dispersion and to improve the accuracy of spin stabilized projectiles in impact locations, by employing a single action drag brake. Reference is made, for example, to U.S. Pat. Nos. 6,345,785 and 5,816,531. In this application, the munition is intentionally fired “too-long,” such that if uncorrected, the projectile would fly past the intended target. Then, while in flight, the controller would determine the best time for the drag brake to be deployed.
Incorporating guidance into artillery rounds increases the cost of the entire system. Gun-hardened, inertial measurement systems are relative costly. Similarly, a significant cost driver is the gun-hardening of components and electronics (e.g., GPS) to survive the loads of gun-launching and to improve the flight path accuracy.
GPS denial is a modern concern, between land/space based intentional jamming of signals by adversarial actors, solar activity also can prevent GPS signals from being received or correctly interpreted. However, should the electronics on-board the projectile be duds, then the projectile will fly past the intended target and potentially cause collateral damage. For obscurant or illumination, it would be beneficial to have a very low cost round that allows soldier assistance without prohibitive expenses.
There is therefore a need for a projectile that is capable of autonomously self-correcting its course toward an intended target, during flight. The projectile should be capable of being nominally aimed at the target, and of maintaining improved accuracy relative to a conventional round. The projectile should not require overshoot adjustment. The projectile should be capable of being deployed at a less full or optimal deployment, so that in the event of electronics or mechanism failure to maneuver the nominal flight, the projectile would follow the flight trajectory of a conventional projectile, including the standard statistical impact dispersion around the target location.
The need for such a course, self-correcting projectile has heretofore remained unsatisfied.